Rollup type doors are widely used in many applications for forming a closure over an opening in a building. Rollup type doors are typically characterized by flexible curtain-like closure members which are adapted to be wound onto a rotatable drum for moving the door between a closed position and an open position. Flexible curtain rollup doors do, however, require reinforcement to prevent windloads from blowing the curtain out of opposed guide tracks or channels and through the door opening. Such reinforcements may include plural spaced apart windlock members disposed above the curtain edges, a thickened portion of the opposed edges of the curtain or one or more spaced apart laterally extending windbar members disposed adjacent to the door curtain and guided in opposed guide tracks.
However, in many industrial applications of rollup type doors it is also desirable: to provide for releasing the aforementioned windbars or windlocks under impact loads which are often encountered by such doors being impacted by freight-moving vehicles, such as lift trucks, for example. Moreover, such doors are also desirably adapted to release from opposed door edge guides at a predetermined air pressure differential or “windload” to prevent catastrophic failure of the door and its associated support structure. Flexible curtain type doors have been developed which include windbars or windlocks at opposite lateral edges of the door which provide for completely releasing the door from its opposed guides. However, releasing the door at both side edges from the associated guide structure complicates the requirements for reinserting the door curtain in the guide tracks. Still further, certain prior art doors which are provided with side edge windlocks and also are provided with laterally extending reinforcing or stiffening members., often called windbars, are somewhat complicated.
Various other desiderata have been recognized in industrial rollup doors including improvements in the door bottom edge seal, or so called bottom bar, wherein it is desirable to provide weighting structure operable to assist in pulling the door toward a closed position while at the same time configuring the weighting structure so that it will not damage an object upon which the door may inadvertently close.
Still further, it is desirable to provide an uncomplicated and inexpensive design which still meets all of the desiderata and trouble-free operation for rollup type doors. It is to these ends that the present invention has been developed.